1. Field of the Invention
The present invention relates to an optical branching device and an optical communication system including the same.
2. Related Background Art
For providing an FTTH (Fiber To The Home) service which enables optical communications between one transmitter station and a plurality of subscribers, an optical communication system known as a so-called PON (Passive Optical Network) system in which the subscribers share a single optical fiber through a multistage of optical splitters as shown in FIG. 1, for example, has conventionally been brought into reality.
That is, the PON system shown in FIG. 1 comprises a terminal station 1 (transmitter station) which is the last relay station of an existing communication system such as the Internet and an optical fiber network laid between the terminal station 1 and subscribers' homes 2 (subscribers). The optical fiber network is constituted by closures (each including an optical branching device 30) provided as branching points, optical communication lines 12 from the terminal station 1 to the closures, and optical communication lines 31 from the closures to the individual subscribers' homes 2.
The terminal station 1 comprises a station-side terminating unit 10 (OLT: Optical Line Terminal) and an optical branching device 11 for branching a multiplexed signal from the OLT 10. On the other hand, each subscriber's home 2 is provided with a subscriber-side terminating unit 20 (ONU: Optical Network Unit). In the closure serving as a branching point of the optical fiber network laid between the terminal station 1 and subscriber's home 2, at least the optical branching device 30 for further branching the multiplexed signal having arrived there and a wavelength selective filter for restricting service contents are arranged.
Since the optical branching devices 11, 30 are disposed within the terminal station 1 and the closure arranged on the optical fiber network, respectively, one station-side terminating unit 10 can provide a plurality of subscribers with FTTH services in the PON system shown in FIG. 1. For branching the multiplexed signal into a number of subscribers' homes 2, a number of optical branching devices are used in this PON system. Therefore, optical branching devices which can be mass-produced inexpensively and installed easily are desired.